Physical Society Colloquium

Adventures in atomic aggregation

Kevin Robbie

Queen's University

The conceptually simple experiment of sequentially depositing atoms onto a flat surface can yield surprisingly complex results. The resulting thin film coatings are seen to depend strongly, in structure and physical behaviour, on the arrival geometry of condensing atoms, in addition to the manifest dependence on chemistry, temperature, etc. Dynamic control of geometry during the growth of thin films, particularly under conditions of glancing vapour incidence, allows atomic-scale engineering of uniquely structured matter, exhibiting anomalous birefringence[1], chiral optical activity[2], magnetic anisotropy; and likely bioactivity, novel superconductivity and more.

In this talk we examine the origin of morphological structure in atomically aggregated materials, and question their usefulness as a nano-technology. Specific examples discussed will include: molecular ordering and light switching in a hybrid liquid crystal device, interference filters with continuously varying refractive index (including a graded-index infrared antireflection coating), highly anisotropic magnets, nanostructured silicon with an absolute birefringence of 0.4 (the largest ever reported), and noble-metal `pyramids' that arise through an as-yet unexplained mechanism. Atomic granularity is seen to play a central role in the emergence of complex form in these structures, suggesting that fundamental questions of predictability and chaos might be probed with this experiment.

[1] G. Beydaghyan, K. Kaminska, T. Brown, and K. Robbie, Enhanced birefringence in vacuum evaporated silicon thin films, Applied Optics 43 (2004) 5343-5349.
[2] K. Robbie, M.J. Brett, and D.J. Broer, Chiral thin film/liquid crystal hybrid materials, Nature 399 (1999) 764-766.